When you buy through links on our articles, Future and its syndication partners may earn a commission.It turns out interstellar comet 3I/ATLAS was almost called 3I/Rubin, after researchers found that the giant survey telescope coincidentally spotted this visitor from the stars over a week before it was officially discovered.3I/ATLAS was officially identified on July 1, 2025 by the Asteroid Terrestrial-impact Last Alert System (ATLAS), which is a network of robotic telescopes in Hawaii, Chile and South Africa. But ten days before, the Vera C. Rubin Observatory, which is also in Chile, began its science validation phase ahead of entering full operation later that year. The science validation phase was designed to calibrate the 27.6-foot (8.4-meter) telescope and its instruments, to ensure that they were working correctly.AdvertisementAdvertisementCurious as to whether Rubin had seen 3I/ATLAS before its official discovery date, a team led by Colin Orion Chandler of the University of Washington went sifting through the data from Rubin’s commissioning phase. Lo and behold, they found that Rubin had imaged 3I/ATLAS on its very first night of taking practice images, on June 20, ten days before ATLAS spotted it.It wasn’t an easy task. Today Rubin has a very well planned out routine — called a ‘pipeline’ — for taking data and processing it for astronomers, but back during the validation phase the pipeline was not in operation. This meant that Chandler and his team had to devise their own custom pipeline to access the data.Chandler estimates that if Rubin had begun its science validation phase a few weeks earlier, its data-handling pipelines might have been up and running in time to snag 3I/ATLAS before July 1.The researchers found that Rubin proceeded to image the interstellar comet a further nine times between June 21 and July 2, and several more times between July 2 and July 20. The images clearly show that 3I/ATLAS was active even before ATLAS detected it, with an obvious coma — a cloud of dust and gas around the head of a comet th …
